Correspondence, business records, diplomatic records, articles, lectures, and other writings, reference and bibliographic notes, drawings, maps, scrapbooks of clippings, and other papers relating to Squier's diplomatic career as U.S. chargé d'affairs in Central America (1849-1858), U.S. commissioner to Peru (1863-1865), and Honduran consul general in New York, N.Y. (1863-1873). Includes material pertaining to the Honduran legation in Washington, D.C. (chiefly 1860-1863) and particularly to the Honduras Interoceanic Railway Company (1853-1870). Also documents Squier's studies and writings in archaeology and ethnology and includes material pertaining to the American Ethnological Society and the New York Anthropological Society. Topics include architecture, hieroglyphics, languages, Indians, and other aspects of archaeological sites in Latin American, the Mississippi Valley, and New York.

Correspondents includes Louis Agassiz, León Alvarado, Henry B. Anthony, John Russell Bartlett, Samuel Birch, E. H. Davis, Joseph Barnard Davis, George R. Gliddon, Joseph Henry, José de Marcoleta, Matthew Fontaine Maury, Brantz Mayer, Luis Molina, Charles Eliot Norton, Josiah Clark Nott, Frederick Ward Putnam, Henry Shelton Sanford, Buckingham Smith, Henry Stevens, John Cresson Trautwine, William Wadden Turner, and Thomas Wright.